Critical reappraisal of DBS targeting for movement disorders

Deep brain stimulation (DBS) is used as a surgical treatment of movement disorders such as Parkinson's disease, dystonia and essential tremor. Fundamental understanding of DBS effects on the pathological neural circuitry remains insufficient. In 2002 DBS of the subthalamic nucleus (STN) and the globus pallidus internus (GPi) was approved for use in patients with PD. Next year, DBS of Gpi and STN for dystonia received a Humanitarian Device exemption from the FDA. The commonly targets for DBS are subthalamic nucleus (STN) or globus pallidus internus (GPi) for Parkinson's disease, Gpi for dystonia and ventro-intermediate (VIM) nucleus of the thalamus for essential tremor. However, VIM DBS cannot sufficiently improve akinesia and rigidity. Pedunculopontine nucleus (PPN) is currently investigated as potential target to improve gait and posture. It is determined that DBS sometimes influences not only motor functions but also the cognitive and affective functions of patients. In this article we review the present state of DBS for movement disorders, appropriate indications, practical effects and stimulation-induced adverse events established in previous studies. We discuss target selection and the effect of DBS on motor and non-motor symptoms of Parkinson's disease, dystonia and essential tremor.